The present invention relates to a ball-point in which is used a cemented carbide containing tungsten carbide, titanium carbide, nickel, molybdenum and chromium.
Some pen balls are used with water based inks. Such inks are corrosive and therefore the pen balls must be resistant to corrosion. The most severe corrosive situation occurs when the pen is stored and the ball is not in use. In that situation both crevice corrosion as well as galvanic corrosion might occur due to the different metals present in the ball and the seat. The thin space in between the ball and the seat is also unfavourable from a corrosion point of view, due to the difference of oxygen potentials between the ink and the exterior of the pen. The corrosive situation is thus rather complex and as the pen should create good writing after some years of storage, the ball must have good corrosion resistance. Furthermore, pen balls must have high hardness in order not to wear when rotating in the seat. The ball material must also be easy to lap during production to make its surface smooth and the diameter within well controlled tolerances. Thus, both strength and toughness is needed for the ball to withstand pressures during lapping.
U.S. Pat. No. 3,503,692 discloses WCxe2x80x94Co cemented carbide or cermets as a material for penballs. In the former case a substoichiometric carbon content is used. In the latter case one or more carbides of Cr, Ta, Nb, W and Ti are bonded together with a nickel or nickel alloy binder phase.
U.S. Pat. No. 3,746,456 discloses a pen ball material consisting of WC or TiC in a binder of Co, Ni, Cr, Pt and Fe.
A cemented carbide, which fulfils the conditions described above, has been prepared and characterized. The cemented carbide contains tungsten carbide, titanium carbide, nickel, molybdenum and chromium. The composition of the cemented carbide provides good resistance to corrosion as well as a high hardness and wear resistance. These properties are particularly interesting for the manufacture of pen balls, for the ball-point pen balls made with these materials will have steady writing characteristics over a long period of time. This material is particularly suitable when water based inks are used, because these inks are far more corrosive than oil based inks.
Accordingly, a first aspect of this invention provides a cemented carbide ball-point pen ball having, in wt %: 80-90 WC, 5-15 TiC and 7-10 binder phase, which has the following composition, in wt %: 10-60 Ni, 0-30 Co, wherein the total amount of Ni and Co is 40-60,  less than 20 Mo, and 15-40 Cr.
A second aspect of this invention provides a cemented carbide ball-point pen ball consisting of in wt %: 80-90 WC, 5-15 TiC and 7-10 binder phase of the following composition, in wt %: 40-60 Ni,  less than 20 Mo, 15-40 Cr, wherein up to 30 Ni may be replaced by Co.
A further aspect of this invention provides the use of a cemented carbide with composition of, in wt %: 80-90 WC, 5-15 TiC and 7-10 binder phase, which has the following composition, also in wt %: 10-60 Ni, 0-30 Co, wherein the total amount of Ni and Co is 40-60,  less than 20 Mo, 15-40 Cr.